METHOD AND SYSTEM FOR MULTI-STAGE CALCINING OF GYPSUM TO PRODUCE AN ANHYDRITE PRODUCT

Description

Background and Summary

[0001] This invention relates to methods and devices for calcining gypsum material, and more particularly, to a method and system for calcining gypsum to recover calcium sulfate anhydrite which is often referred to, in insoluble form, as "dead burn".

[0002] Many methods and devices for calcining gypsum are well known. Traditionally, refractories have been used to calcine gypsum in large kettles having a thickened dome-shaped bottom, and the kettle is heated by gas-fired flames in a brick refractory structure. (See U.S. Patent No. 3,236,509). However, using a refractory to calcine gypsum results in an extreme waste of energy due to the excessive amount of heat which must be applied to the kettle to heat the gypsum contained therein, and the refractory brick enclosure is also inefficient since it has a large footprint and occupies valuable factory space. Other calcining methods and devices have taken the form of refractoryless kettles which use submerged combustion heating systems within the kettle such as disclosed in U.S. Patent Nos. 4,626,199, 4,629,419 and 4,744,961. One major objective of both refractory and refractoryless kettles for calcining gypsum has been to produce calcium sulfate hemihydrate, better known as stucco, for use in the production of wallboard.

[0003] US 4247518 relates to an apparatus for producing calcium sulfate hemihydrate. The apparatus comprises a series of interconnecting fluidized bed compartments each containing a heat exchanger, the temperature of each subsequent compartment being greater than that of the preceding compartment.

[0004] US 4974334 relates to an apparatus for drying and/or calcining gypsum, primarily for producing calcium sulfate hemihydrate. The apparatus comprises a series of interconnecting heated treatment areas, the temperature of each subsequent treatment area being greater than that of the preceding area. Each treatment area is provided with a base which can vibrate, and through which gas can flow.

[0005] In contrast to such prior art methods which were concerned with production of hemihydrate or stucco, the method and system of this invention are concerned primarily with recovering gypsum material from the calcining process which consists essentially of calcium sulfate anhydrite. The recovered anhydrite product may be in the form of soluble calcium sulfate anhydrite which is slightly unstable or more preferably is recovered in the form of insoluble calcium sulfate anhydrite which is stable and often referred to as dead burn. Dead burn material has many applications including as a filler in thermoplastics, herbicides, foods and pharmaceuticals, cement, plaster additives, etc. However, the production of dead burn is difficult.

[0006] Raw gypsum is generally in the form of a dry powder and takes the form of CaSO₄·2H₂O. When raw gypsum is heated to a temperature of generally about 250° F.- 380° F. or even higher, the powder converts to hemihydrate which takes the form of CaSO₄·½H₂O + 1½H₂O. The 1½H₂O is in the form of water vapor and fluidizes the dry powder during the calcining process so that it will flow through the apparatus. When the hemihydrate is heated to even higher temperatures, the gypsum converts to soluble anhydrite or insoluble anhydrite CaSO₄ (dead burn). However, the ½H₂O released during conversion to soluble or insoluble anhydrite does not fluidize the powder very well.

[0007] Due to such fluidization problems, conventional refractory or refractoryless calcining methods to produce dead burn have been less than effective in efficiently and economically producing dead burn. Specifically, using a refractory for producing dead burn material is excessively expensive and cost prohibitive due to required temperatures of about 480°C to 710°C (about 900° F. to 1300° F).

[0008] The prior art refractoryless methods of calcining gypsum are more economical than using a refractory but are impractical for producing dead burn material due to fluidization problems. In addition, the anhydrite produced from such systems is often not evenly heated and still contains substantial amounts of chemically-combined water which make the anhydrite unsuitable as a filler for thermoplastics and other similar applications.
Other methods of calcining gypsum to produce dead burn have included using flash calciners to produce dead burn. Such flash calciners entrain the ground gypsum in a stream of accelerated air which is then flash heated to elevated temperatures. However, such systems are limited in their capacity and flowthrough rate.

[0009] Accordingly, the present invention provides a method of calcining gypsum to produce an anhydrite product, said method comprising the steps of feeding ground gypsum into a first kettle, heating the ground gypsum in said first kettle to a first predetermined temperature, overflowing said ground gypsum from said first kettle into at least one subsequent kettle, heating said gypsum in said at least one subsequent kettle to a final temperature higher than said first predetermined temperature while simultaneously fluidising said gypsum in said at least one subsequent kettle and recovering said gypsum from said at least one subsequent kettle which consists essentially of calcium sulfate anhydrite, said step of fluidising said gypsum in said at least one subsequent kettle comprising providing at least one rotatable blade having a plurality of injection ports along a leading edge thereof within said at least one subsequent kettle and moving said at least one blade within said at least one subsequent kettle while simultaneously discharging a fluidising medium through said plurality of injection ports to fluidize said gypsum in said at least one subsequent kettle.

[0010] An important aspect of this invention therefore lies in providing a method for producing dead burn material in a cost effective and efficient manner which avoids the excess cost of a refractory and overcomes the fluidization problems which would otherwise occur in using prior art methods of calcining gypsum to produce dead burn. Such a method involves feeding the gypsum material through two or more stages of calcining to gradually convert the gypsum to dead burn material. In the first stage, the gypsum material contains chemically-combined water which is released by the heating process to self-fluidize the gypsum powder so that it will flow through the apparatus. The gypsum powder in the first stage is generally heated to form a hemihydrate product which occurs in a temperature range of about 120°C to 190°C (about 250°F. - 380°F.), or generally less than 200°C (400°F.)

[0011] The material is then passed through at least one subsequent stage, preferably two or more stages, so that it is heated sufficiently to form calcium sulfate anhydrite. In the subsequent stages, the method includes the steps of heating and simultaneously fluidizing the material with a fluidization media, preferably air, so that it will flow through the subsequent stages of the system. The material is then recovered from the process in a form consisting essentially of calcium sulfate anhydrite. The recovered anhydrite product may be soluble or insoluble depending upon the desired application, and the insoluble anhydrite is generally referred to as dead burn material. For purposes of convenience, the term gypsum is generally used herein to describe the various forms of calcium sulfate, including dihydrate (gypsum), hemihydrate (stucco) and anhydrite (dead burn).

[0012] In one preferred embodiment of the method of this invention, the method involves three steps of calcining the gypsum through three calcining kettles to recover calcium sulfate anhydrite from the third kettle. In particular, the method comprises the steps of first feeding ground gypsum into a first kettle and heating the gypsum to a first predetermined temperature of about 120°C to 190°C (about 250°F. - 380°F.) preferably about 150°C (about 310°F.) The gypsum
powder is in a hemihydrate state at such a temperature and the release of water vapor, by the reaction CaSO₄·2H₂O → CaSO₄·½H₂O + 1½H₂O, sufficiently fluidizes the powder so that it will flow through the process. The next step is to overflow the heated gypsum from the first kettle into a second kettle. The material in the second kettle is then heated to a second predetermined temperature and simultaneously fluidized with a fluidizing media, preferably air, in the second kettle. The second predetermined temperature is about 260°C to 430°C (about 500°F. - 800°F.), preferably about 320°C (about 600°F.). At such a temperature, the gypsum material will be a multi-phase material having relatively poor flow characteristics. However, the fluidization of the gypsum powder with a fluidizing media in the second kettle ensures that it will properly flow through the system. The gypsum powder is then overflowed from the second kettle into a third kettle where it is then heated to a third predetermined or final temperature and simultaneously fluidized with a fluidizing media. The gypsum powder is then recovered from the third kettle as a gypsum material consisting essentially of calcium sulfate anhydrite. In a method to produce insoluble calcium sulfate anhydrite or dead burn, the third predetermined or final temperature should be greater than about 480°C (about 900°F.), preferably greater than about 500°C (about 930°F.), to ensure the production of dead burn material. Generally, the third predetermined temperature should be in the range of about 480°C to 710°C (about 900°F. - 1300°F.), and in one embodiment of the invention, the third predetermined temperature is about 540°C (about 1000°F.).

[0013] The step of fluidizing the gypsum powder in the second and third kettles includes providing a fluidization means in those kettles for fluidizing the gypsum material contained therein.
Preferably, the mixing blades include a pair of horizontally-extending blades, and a pair of oppositely-oriented, helically-twisted blades which extend vertically between the first and second horizontal blades. The helical blades each include a leading edge, a trailing edge and a breaking edge, and the air pipes are positioned along the breaking edges with the injection ports directed towards the burner coils. The blades are preferably arranged around a central axle, and an air source may be connected to the central axle which is then connected with the air pipes along the leading edges of the helical blades.

[0014] In a preferred embodiment, the fluidization means also includes a plurality of radially-arranged air injection nozzles positioned about a periphery of the kettle shells of the second and third kettles. Each air injection nozzle includes a plurality of air injection ports, and the nozzles are each connected to a pressurized air line for injecting pressurized air through the ports and into the contents of the kettle. The pressurized air sufficiently fluidizes the ground gypsum at elevated temperatures so that it will adequately flow through the system.

[0015] In an alternate construction, the fluidization means may include a perforated screen and a woven web or mat positioned in the bottom of the second and third kettles and a pressurized air chamber located below the screen and mat for injecting air through the screen and mat and into the interior of the kettle. Air is blown into the air chamber and through the screen and mat throughout the gypsum material at elevated temperatures so that the ground gypsum material will flow through the second and third stages of the apparatus.

[0016] The fluidization means is preferably formed of the combination of the helical mixing blades and air pipes along the leading edges of those blades as well as a plurality of radially-arranged air injection nozzles. However, the air injection nozzles may be replaced with use of an air chamber and perforated sheet and web in the bottom of the kettles. The fluidization means may also take a variety of other forms of means for fluidizing or aerating the gypsum powder in the kettles during the second and third stages when the gypsum powder does not sufficiently self-fluidize.

[0017] Other objects, features, and advantages will become apparent from the following description and drawings.

Brief Description of the Drawings

[0018] 

FIG. 1 is a side, partially fragmentary, elevational view illustrating a three-stage kettle construction for use in the method of the present invention.

FIG. 2 is a side, partially sectional, elevational view illustrating the interior of the first kettle of the calcining system shown in FIG. 1.

FIG. 3 is an exploded elevational view illustrating one embodiment of the fluidization means for the second and third kettles of the calcining system shown in FIG. 1.

FIG. 4 is a schematic, cross-sectional, top view of an alternate embodiment of the fluidization means for the second and third kettles of the calcining system shown in FIG. 1.

FIG. 5 is a schematic side view of the fluidization means shown in FIG. 4.

FIG. 6 is an enlarged sectional view of one of the nozzles of the fluidization means shown in FIGS. 4 and 5.

FIG. 7 is a front sectional view of the nozzle shown in FIG. 6.

FIG. 8 is a top, partially sectional, view of another embodiment of the fluidization means for the second and third kettles of the calcining system shown in FIG. 1.

FIG. 9 is a side elevational view, partially in section, illustrating the alternate embodiment of the fluidization means shown in FIG. 8.

Detailed Description of the Preferred Embodiments

[0019] Referring to the drawings, the numeral 10 generally designates a multi-stage calcining system for use in the method of the present invention. In embodiment given in the drawings, the multi-stage calcining system 10 includes a first kettle 11, a second kettle 12, and a third kettle 13. Each of the kettles is designed for calcining gypsum and many of the details of the construction and operation of such kettles are fully disclosed in co-owned pending application No. 08/382,612, filed on February 2, 1995, entitled "Method and Apparatus for Continuous Refractoryless Calcining of Gypsum", which is hereby incorporated by reference. However, it will be understood that other types of kettles may be used. The method and system of this invention must include at least two stages of calcining and include two or more kettles. In the embodiment shown in the drawings, the system 10 includes three kettles 11-13 for three stages of calcining and in one embodiment, each of the kettles has a height of about 5½ feet and a diameter of about 5½ feet. However, it will be understood that four and five stages of calcining or other embodiments of two or more stages may be used in practicing the invention which is not limited to any particular calcining system or number of stages.

[0020] Referring to FIG. 1, each of the kettles 11-13 includes a kettle shell 14, an internal coil-type burner tube assembly 15, and an external immersion tube burner 16. The burner tube coils 15 are supported by brackets 17 within kettle shells 14 and are arranged in a spiral fashion for uniformly heating the gypsum material contained therein. The immersion burners 16 are gas-fired burners which project a flame into the burner tubes 15, and the heat rises within the tubes so that the heated media, typically combustion gases and air, flows through the tubes to uniformly heat the contents of the kettle shells 14. Such gas-fired immersion tube burners are commercially available from many sources, including Pillard Combustion (Procedair) of Montreal, Quebec, Canada; Eclipse Combustion of Rockford, Illinois; Maxon Corporation of Muncie, Indiana; and Hauck Manufacturing Co. of Lebanon, Pennsylvania. Currently, such gas-fired immersion tube burners have a capacity limitation of about 5,000,000 BTU and the particular capacity of the selected burners 16 will depend upon the desired output temperature of the particular kettle and the interior capacity of the kettle, among other factors. In one embodiment, each of the immersion tube burners had a capacity of 5.3mm/BTU/hr. Such immersion tube burners 16 can be run on a variety of fuels, including liquified petroleum or natural gas. However, use of fuels such as coal or oil should be avoided since the exhaust gases from the flames of such fuels may leave an unwanted interior coating or residue on the interior of the burner tubes 15. While it is believed that the use of such gas-fired immersion tube burners 16 is preferable, other heat sources for circulating a heated media, such as steam, oil or the like, could be used for circulating a heated media through the burner tube coils 15 and heating the kettle contents. While such alternate sources of heat may be used, such sources must be capable of obtaining a final temperature of the gypsum powder of greater than 480°C (900°F.), preferably above 500°C (930°F.), to convert the gypsum powder to insoluble calcium sulfate anhydrite or dead burn. It will also be understood that the method of this invention can be used with many types of such refractoryless calcining kettles and that the method is not limited to operation with any one particular type of refractoryless calcining kettle.

[0021] Referring to FIGS. 1 and 2, a conventional feed conveyor 18 is provided over an input riser 19 in first kettle 11 for feeding ground gypsum powder 20 into first kettle 11. Mixing means are also provided in the first kettle 11 for mixing the ground gypsum contained therein so as to avoid dead spots in the heating of the ground gypsum. In the embodiment given in FIGS. 1 and 2, the mixing means take the form of a central shaft 21 mounted on bearings 21a and 21b and connected to a drive means 22 for rotating shaft 20. Shaft 20 includes a plurality of horizontally-extending mixing blades 23, 24 and 25 for mixing the ground gypsum contained in the first kettle 11. Each of the first, second and third kettles 11-13 are shown in FIG. 1 as including such a mixing means for mixing the kettle contents. However, it will be understood that the mixing means may take various forms and may be omitted or be of significantly different construction in the second and third kettles 12 and 13 in some constructions as will be described in more detail hereinafter.

[0022] In operation, the feed conveyor 18 feeds ground gypsum 20 through riser 19 into first kettle 11, and the burner 16 and the burner tubes 15 in first kettle 11 heat the ground gypsum contained therein to a first predetermined temperature. The gypsum is heated in first kettle 11 to a temperature of about 120°C to 190°C (about 250°F. - 380°F.), preferably about 150°C (about 310°F.). Such heating of the gypsum powder causes it to be self-fluidized by the water vapor released from the reaction of CaSO₄·2H₂O → CaSO₄·½H₂O + 1½H₂O so that the powder will adequately flow out of first kettle 11 and through the system. When first kettle 11 is so heated, the released water vapor and the addition of more gypsum powder causes the heated gypsum material to overflow through an overflow tube 26 from first kettle 11 into second kettle 12. Generally, the material which is overflowed from the first kettle 11 into the second kettle 12 is in the form of calcium sulfate hemihydrate. However, for purposes of convenience, the various forms of calcium sulfate, including dihydrate, hemihydrate and anhydrite, will be generally referred to as gypsum material or powder to simplify the discussion.

[0023] When the ground gypsum fills the second kettle 12, the burner 16 and burner tube 15 in second kettle 12 heat the ground gypsum contained therein to a second predetermined temperature of about 260°C to 430°C (about 500°F. - 800°F.), preferably about 320°C (about 600°F). The gypsum material at the second predetermined temperature will be a multi-phase product containing very little chemically-combined water and having poor flow characteristics due to absence of released water vapor such as in the first kettle 11. However, as will be described in more detail hereinafter, the second kettle 12 is provided with fluidization means for fluidizing the gypsum in the second kettle 12 with a fluidization media, preferably air, so that it will flow through the apparatus. When heated in kettle 12, the gypsum overflows through overflow tube 27 from second kettle 12 and into third kettle 13.

[0024] The ground gypsum flowing through overflow tube 27 fills third kettle 13, and burner 16 and burner tubes 15 in third kettle 13 heat the ground gypsum contained therein to a third predetermined temperature of about 480°C to 710°C (about 900°F. - 1300°F.), preferably about 540°C (about 1000°F.). The third predetermined temperature should be greater than 480°C (900°F.), preferably greater than 500°C (930°F.), to ensure that the recovered gypsum from third kettle 13 will consist essentially of insoluble calcium sulfate anhydrite or dead burn material. However, the third predetermined temperature should generally not exceed 710°C (1300°F.) by any significant amount such as would cause the anhydrite to disassociate to lime. The dead burn material is then recovered from third kettle 13 by overflowing it through a third overflow tube 28 and into a suitable receptacle. If desired, the ground gypsum recovered from the third kettle 13 may consist essentially of soluble calcium sulfate anhydrite, and a third predetermined temperature should be lower than 480°C (900°F.) if production of soluble anhydrite is desired. Due to the elevated temperatures in the third kettle, the ground gypsum will have poor flow characteristics and the third kettle 13 is also provided with fluidization means for facilitating flow of the ground gypsum through the apparatus. The fluidization means provided in the second and third kettles 12 and 13 may be the same or different as will be described in more detail hereinafter.

[0025] Referring to FIG. 1, each of the first, second and third kettles 11-13 has a discharge tube 29 running from a bottom of the kettle to the overflow tubes 26, 27 and 28, respectively. The discharge tubes 29 are provided only for emptying the kettles 11-13 when the process is shut down, and the overflow tubes 26-28 are the primary means for transferring the gypsum powder from one kettle to another. While the overflow tubes 26 and 27 are shown as leading directly from first kettle 11 to second kettle 12 and from second kettle 12 to third kettle 13, it will be understood that other communication means between the kettles could be used. For example, the overflow tubes 26 and 27 could discharge onto a conveyor system which would then transport the gypsum to an input riser of the subsequent kettle.

[0026] The fluidization means in the second and third kettles 12 and 13 may take the form of various constructions for ensuring that the ground gypsum material, when it is heated to the second and third predetermined temperatures, will flow through the calcining apparatus or system 10. The fluidization means may include a number of different means for fluidizing the gypsum powder and varying combinations thereof. Three different methods or systems of fluidizing the gypsum powder will now be described, in connection with FIG. 3, FIGS. 4-7, and FIGS. 8-9, respectively. The preferred combinations of the different fluidization means will then be described.

[0027] In the construction shown in FIG. 3, the fluidization means includes a perforated sheet 30, a woven web or mat 31, and an air chamber 32 provided at the bottom of the second and third kettles 12 and 13. The perforated sheet 30 defines a plurality of apertures 30a and may be made of stainless steel or other heat-resistant materials. The woven mat 31 is formed of a loosely woven web of stainless-steel material or other heat-resistant material. The perforated sheet 30 primarily serves the purpose of protecting the woven mat 31 from being ripped or torn by contact with components which are being placed in the kettle or otherwise. In operation, an air line 33 is used to inject air below the woven mat 31 and perforated sheet 30, and the sheet 30 and mat 31 ensure that the air is uniformly distributed upwards through the ground gypsum material contained in the second and third kettles 12 and 13 to adequately fluidize that material. Preferably, the air injected through the ground gypsum material is preheated utilizing exchanged waste burner gases in a conventional heat exchanger system, and the fluidizing air is preferably heated to a temperature of about 90°C to 260°C (about 200°F. - 500°F.)
In such a construction, the second and third kettles 12 and 13 may include a mixing means as previously described in connection with FIGS. 1 and 2. However, the mixing means is provided in combination with an aeration means as will be described hereinafter in more detail in connection with the embodiment shown in FIGS. 8 and 9.

[0028] In the construction shown in FIGS. 4-7, the fluidization means includes a plurality of air injection nozzles 34 which are radially spaced about a periphery of the kettle shells 14 of the second and third kettles 12 and 13. Each air injection nozzle 34 is connected to a pressurized air line 35, and each of the nozzles 34 defines a plurality of ports 36, including radial ports 36a and axial ports 36b. In the embodiment shown, a first set 37 of a plurality of nozzles 34 are provided circumferentially around the kettle shell 14 at one level while a second set 38 of a plurality of nozzles 34 are provided circumferentially about kettle shell 14 at another level. Both sets 37 and 38 are provided near the bottom of the kettle shell 14, and the air injected near the bottom of the shell 14 helps to force the heated gypsum material upward so that it will overflow into the respective overflow tubes 27 or 28. In such a construction, the second and third. kettles 12 and 13 may include a mixing means as previously described in connection with the embodiment shown in FIGS. 1 and 2. However, the mixing means includes an aeration means as described in more detail hereinafter in connection with the embodiments shown in FIGS. 8 and 9.

[0029] In the construction shown in FIGS. 8-9, the fluidization means includes a mixing and aeration means combination in which air injection means are provided along the leading edges of the mixing means for fluidizing the ground gypsum in the second and third kettles 12 and 13. In such a construction, the mixing means as previously described in connection with FIGS. 1 and 2 is omitted. In the particular embodiment shown in FIGS. 8-9, the mixing and aeration means combination includes a central axle 39, first and second horizontal blades 40 and 41, and first and second helical mixing blades 42 and 43. The helical mixing blades 42 and 43 extend vertically between the horizontal blades 40 and 41, and a pair of horizontal support bars 44 and 45 extend between central shaft 39 and intermediate portions of the helical mixing blades 42 and 43. Each helical mixing blade 42 and 43 has a breaking edge 42a and 43a, a leading edge 42b and 43b, and a trailing edge 42c and 43c. The blades 42 and 43 are designed to draw the gypsum powder towards the center of the kettle over the leading edges 42b and 43b and towards and then over the trailing edges 42c and 43c. Such a construction causes a void in the gypsum generally behind the blades 42 and 43 and sets up a vortex effect in the gypsum in the kettle. In addition, such a construction draws the gypsum powder off of, and exposes, the burner tube coil 15 which is located radially outwardly from the blades 42 and 43. Preferably, the injection ports 48 are directed toward the burner tube coil 15 to blow the gypsum powder off of the burner tube 15 when it is exposed by the vortex effect which draws the powder towards the center of the kettle.

[0030] Each of the helical blades 42 and 43 is provided with an air pipe 46 and 47 along its breaking edge 42a and 43a, respectively. Each of the air pipes 46 and 47 includes a plurality of radially-directed ports 48 for injecting air into and fluidizing the kettle contents. The pressurized air is supplied to air pipes 46 and 47 by a line 49 connected to an internal passage 39a in shaft 39, and internal passage 39a is connected to air pipes 46 and 47 via passages 44a and 45a in support members 44 and 45. While a particular embodiment of mixing blades having air injection means along their breaking edges has been shown for purposes of illustration, it will be understood that the configuration of the mixing blades and the positioning of the air pipes and radially-directed ports may vary considerably.

[0031] In a preferred embodiment, the fluidization means preferably includes the fluidization means shown in FIGS. 4-7 and the fluidization means shown in FIGS. 8-9. Specifically, the second and third kettles 12 and 13, or all subsequent kettles after the first kettle 11, include both a plurality of air injection nozzles 34 about a periphery of the kettle shell 14 as well as mixing blades 42 and 43 having air injection pipes 46 and 47 along their breaking edges 42a and 43a for injecting air into the gypsum. Such a fluidization means combination ensures that the gypsum powder will be adequately fluidized with the fluidizing media, preferably air, during processing through the second and third kettles or any kettles subsequent to the first kettle. However, it will be understood that the fluidization means may take various forms.

[0032] The method of this invention to calcine gypsum to produce an anhydrite product will now be described in connection with the particular apparatus shown in the drawings. The ground gypsum 20 is first fed into first kettle 11 using conveyor 18 and input riser 19, and the ground gypsum is then heated in the first kettle 11 to a first predetermined temperature of about 120°C to 190°C (about 250°F. - 380°F.), preferably 150°C (310°F). The heated ground gypsum is then overflowed through overflow pipe 26 from first kettle 11 into second kettle 12. The ground gypsum in second kettle 12 is then heated to a second predetermined temperature higher then the first predetermined temperature while simultaneously fluidizing the gypsum in the second kettle 12. The second predetermined temperature is about 260°C to 430°C (about 500°F. - 800°F.), preferably about 320°C (about 600°F), and the ground gypsum at that temperature will be a multi-phase product. The ground gypsum is then overflowed from second kettle 12 through overflow pipe 27 and into third kettle 13. The ground gypsum in the third kettle is then heated to a third predetermined temperature higher than the second predetermined temperature and simultaneously fluidized within the third kettle. The third predetermined temperature is preferably greater than 480°C (900°F.), preferably greater than 500°C (930°F.), to ensure that an insoluble anhydrite or dead burn product is recovered from the third kettle. The third predetermined temperature should fall within the range 480°C to 710°C (900°F. - 1300°F.) for producing dead burn and is preferably about 540°C (about 1000°F.). The ground gypsum which is recovered from the third kettle consists essentially of calcium sulfate anhydrite in the form of insoluble anhydrite product or dead burn material, or if desired, may be soluble anhydrite if the third or final temperature is below 900° F. The recovered material is then sent by a conventional conveyor or the like to conventional means for cooling and packaging (not shown). The fluidization of the gypsum in the second and third kettles 12 and 13 may be accomplished in various ways, and the fluidization means in the second and third kettles may be the same or different.

[0033] In the preferred embodiment, the mixing blades include air injection pipes along their leading edges for fluidizing the kettle contents. In addition, the fluidization means also includes, in the preferred embodiment, a plurality of air injection nozzles 34 about a periphery of the kettle shell 14 to further fluidize or aerate the powdered gypsum in the second and third kettles 12 and 13. In one embodiment with three kettles as shown, the system was designed to have a flowthrou g h rate of 4 tons per hour and is currently being run at 2 tons per hour.

[0034] The method of this invention provides an efficient and effective method for recovering gypsum which consists essentially of calcium sulfate anhydrite from a calcining process without the expense of a refractory. By providing a fluidization means in the second and third kettles, or any subsequent kettles past the first kettle, the method overcomes problems with fluidization associated with many prior art devices.

Claims

1. A method of calcining gypsum to produce an anhydrite product, said method comprising the steps of:

feeding ground gypsum into a first kettle;

heating the ground gypsum in said first kettle to a first predetermined temperature;

overflowing said ground gypsum from said first kettle into at least one subsequent kettle;

heating said gypsum in said at least one subsequent kettle to a final temperature higher than said first predetermined temperature while simultaneously fluidizing said gypsum in said at least one subsequent kettle; and

recovering said gypsum from said at least one subsequent kettle which consists essentially of calcium sulfate anhydrite,

said step of fluidizing said gypsum in said at least one subsequent kettle comprising providing at least one rotatable blade having a plurality of injection ports along a leading edge thereof within said at least one subsequent kettle and moving said at least one blade within said at least one subsequent kettle while simultaneously discharging a fluidizing medium through said plurality of injection ports to fluidize said gypsum in said at least one subsequent kettle.

2. A method according to Claim 1, characterised by said at least one blade comprising a first helically-twisted blade and a second helically-twisted blade each extending vertically between an upper and lower horizontal blade, and by said first and second helically-twisted blades each including an air pipe along a breaking edge thereof having a plurality of injection ports which are radially-directed for injecting a fluidizing medium into said gypsum material in said at least one subsequent kettle.

3. A method according to Claim 2, characterised by said first and second helically-twisted blades having a leading edge forwardly of said breaking edge and a trailing edge rearwardly of said breaking edge.

4. A method according to Claim 3, characterised by said first and second helically-twisted blades and said upper and lower horizontal blades being mounted on a central axle, and by a pair of first and second horizontal support bars extending between said central axle and intermediate portions of said first and second helically-twisted blades.

5. A method according to Claim 4, characterised by said central axle and said support bars each including air passages, and by an air source which is connected to said air passage in said central axle for distributing air through said air passages and through said injection ports along the breaking edges of said first and second helically-twisted blades.

6. A method according to any preceding claim, characterised by said step of fluidizing said gypsum in said at least one subsequent kettle including providing a woven mat in a bottom of said at least one subsequent kettle and injecting a fluidized medium through said mat and into said gypsum contained in said at least one subsequent kettle.

7. A method according to Claim 6, characterised by a perforated screen which defines a plurality of apertures being provided over said woven mat.

8. A method according to Claim 6 or Claim 7, characterised by said woven mat being formed of stainless steel.

9. A method according to any preceding claim, characterised by said step of fluidizing said gypsum in said at least one subsequent kettle including providing a plurality of air injection nozzles about a periphery of said at least one subsequent kettle and injecting a fluidizing medium through said plurality of nozzles for fluidizing said gypsum in said second and third kettles.

10. A method according to Claim 9, characterised by said air injection nozzles each including radially-directed ports and at least one axially-directed port.

11. A method according to any preceding claim, characterised by said at least one subsequent kettle including a second kettle and a third kettle and by the steps of heating and fluidizing said gypsum including heating said gypsum in said second kettle to a second predetermined temperature higher than said first predetermined temperature and heating said gypsum in said third kettle to a third predetermined temperature higher than said second predetermined temperature, said third predetermined temperature being equal to said final temperature.

12. A method according to any preceding claim, characterised by said final predetermined temperature being greater than about 480°C (about 900° F.).

13. A method according to Claim 12, characterised by said recovered gypsum consisting essentially of insoluble calcium sulfate anhydrite.

14. A method according to any of Claims 1 to 11 characterised by said final predetermined temperature being less than about 480°C (about 900° F.) and by said recovered gypsum consisting essentially of soluble calcium sulfate anhydrite.

15. A method according to any preceding claim, characterised by said first predetermined temperature being less than about 200°C (about 400° F.), and by the ground gypsum which is overflowed from said first kettle consisting essentially of calcium sulfate hemihydrate.

16. A method according to any of Claims 11 to 14, characterised by overflowing said ground gypsum from said first kettle into said second kettle and heating said gypsum in said second kettle to a second predetermined temperature higher than said first predetermined temperature while simultaneously fluidizing said gypsum in said second kettle, by overflowing said gypsum from said second kettle into said third kettle and heating said gypsum in said third kettle to a third predetermined temperature higher than said second predetermined temperature while simultaneously fluidizing said gypsum in said third kettle, and by recovering said gypsum from said third kettle which consists essentially of calcium sulfate anhydrite.

17. A method according to Claim 16, characterised by said third predetermined temperature being greater than about 480°C (about 900° F.) and by said recovered gypsum consisting essentially of insoluble calcium sulfate anhydrite.

18. A method according to Claim 16, characterised by said third predetermined temperature being less than about 480°C (about 900° F.) and by said recovered gypsum consisting essentially of soluble calcium sulfate anhydrite.

19. A method according to any of Claims 16 to 18, characterised by said first predetermined temperature being about 120°C to 190°C (about 250° F. - 380° F.), by said second predetermined temperature being about 260°C to 430°C (about 500° F. - 800° F.), and by said third predetermined temperature being about 480°C to 710°C (about 900° F. - 1300° F.).

20. A method according to Claim 19, characterised by said first predetermined temperature being about 150°C (about 310° F.), by said second predetermined temperature being about 320°C (about 600° F.), and by said third predetermined temperature being about 540°C (about 1000° F.).

21. A system for calcining gypsum and producing an anhydrite product, said system comprising:

at least two refractoryless kettles having a kettle shell defining an interior chamber for retaining ground gypsum, said at least two kettles including a first kettle and at least one subsequent kettle;

heating means disposed in said at least two kettles for circulating a heated medium throughout said interior chamber of said at least two kettles without allowing said heated medium to contact gypsum contained in said at least two kettles;

feeding means for feeding ground gypsum into said first kettle;

communication means for transferring heated ground gypsum from said first kettle to said at least one subsequent kettle; and

fluidization means provided in said at least one subsequent kettle for fluidizing ground gypsum contained therein said fluidization means comprising at least one rotatable blade having a plurality of injection ports along a breaking edge thereof provided in said at least one subsequent kettle and air supply means for injecting a fluidizing medium through said plurality of injection ports to fluidize the gypsum contained in said at least one subsequent kettle.

22. A system according to Claim 21, characterised by said at least one blade comprising a first helically-twisted blade and a second helically-twisted blade extending vertically between an upper and a lower horizontal blade, and by said first and second helically-twisted blades each including an air pipe along the breaking edges thereof having a plurality of said injection ports which are radially-directed in said at least one subsequent kettle for injecting a fluidized medium into said gypsum contained therein.

23. A system according to Claim 22, characterised by said heating means comprising a burner tube coil and by said first and second helically-twisted blades having leading edges forwardly of said breaking edges and trailing edges rearwardly of said breaking edges, said injection ports of said air pipes on said breaking edges being directed towards said burner coil.

24. A system according to Claim 22 or Claim 23, characterised by said first and second helically-twisted blades and said upper and lower horizontal blades being mounted on a central axle, and by a pair of first and second horizontal support bars extending between said central axle and intermediate portions of said first and second helically-twisted blades.

25. A system according to Claim 24, characterised by said central axle and said support bars including air injection passages, and by an air source which is connected to said air passage in said central axle for distributing air through said air passages and through the injection ports along the breaking edges of said first and second helically-twisted blades.

26. A system according to any of Claims 21 to 25, characterised by said fluidization means further comprising a woven web or mat provided in a bottom of said at least one subsequent kettle and an air source for injecting a fluidized medium through said woven web or mat and into gypsum contained in said subsequent kettle(s).

27. A system according to Claim 26, characterised by a perforated screen which defines a plurality of apertures being provided over said woven web or mat.

28. A system according to Claim 26 or Claim 27, characterised by said woven web or mat being formed of stainless steel.

29. A system according to any of Claims 21 to 28, characterised by said fluidization means further comprising a plurality of air injection nozzles disposed about a periphery of the kettle shell(s) of said at least one subsequent kettle, and by air source means connected to said plurality of nozzles for injecting air through said nozzles and into the kettle contents to fluidize the gypsum contained therein.

30. A system according to Claim 29, characterised by said air injection nozzles including a plurality of radially-directed ports and at least one axial port.

31. A system according to any of Claims 21 to 30 , characterised by said at least two kettles comprising a first, a second and a third kettle.

Ansprüche

1. Verfahren zum Kalzinieren von Gips zur Herstellung eines Anhydrit-Erzeugnisses, wobei das Verfahren die Schritte aufweist:

Zuführen von gemahlenem Gips in einen ersten Kessel;

Erwärmen des gemahlenen Gipses in dem ersten Kessel auf eine erste vorbestimmte Temperatur;

Überlaufenlassen des gemahlenen Gipses aus dem ersten Kessel in zumindest einen nachfolgenden Kessel;

Erwärmen des Gipses in dem zumindest einen nachfolgenden Kessel auf eine Endtemperatur, die höher als die erste vorbestimmte Temperatur ist, während gleichzeitig der Gips in dem zumindest einen nachfolgenden Kessel verflüssigt wird; und

Rückgewinnung des Gipses aus dem zumindest einen nachfolgenden Kessel, der im wesentlichen aus Calciumsulfatanhydrit besteht,

wobei der Schritt zum Verflüssigen des Gipses in dem zumindest einen nachfolgenden Kessel das Bereitstellen von zumindest einer drehbaren Schaufel mit mehreren Einspritzöffnungen entlang einer vorauseilenden Kante in dem zumindest einen nachfolgenden Kessel sowie das Bewegen der zumindest einen Schaufel in dem zumindest einen nachfolgenden Kessel umfasst, während gleichzeitig ein Verflüssigungsmedium durch die mehreren Einspritzöffnungen ausgetragen wird, um den Gips in dem zumindest einen nachfolgenden Kessel zu verflüssigen.

2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass die zumindest eine Schaufel eine erste spiralförmig gewundene Schaufel und eine zweite spiralförmig gewundene Schaufel umfasst, die sich jeweils vertikal zwischen einer oberen und einer unteren horizontalen Schaufel erstrecken, und dass die ersten und zweiten spiralförmig gewundenen Schaufeln jeweils ein Luftrohr entlang einer Brechkante umfassen, das mehrere Einspritzöffnungen aufweist, die zum Einspritzen eines Verflüssigungsmediums in das Gipsmaterial in dem zumindest einen nachfolgenden Kessel radial gerichtet sind.

3. Verfahren nach Anspruch 2, dadurch gekennzeichnet, dass die ersten und zweiten spiralförmig gewundenen Schauteln eine vorauseilende Kante vor der Brechkante und eine nacheilende Kante hinter der Brechkante aufweisen.

4. Verfahren nach Anspruch 3, dadurch gekennzeichnet, dass die ersten und zweiten spiralförmig gewundenen Schaufeln und die oberen und unteren horizontalen Schaufeln auf einer zentralen Achse angebracht sind, und dass ein Paar von ersten und zweiten horizontalen Tragstangen sich zwischen der zentralen Achse und zwischen Abschnitten der ersten und zweiten spiralförmig gewundenen Schaufeln erstrecken.

5. Verfahren nach Anspruch 4, dadurch gekennzeichnet, dass die zentrale Achse und die Tragstangen jeweils Luftdurchlässe enthalten, und dass eine Luftquelle vorgesehen ist, die mit dem Luftdurchlass in der zentralen Achse zum Verteilen von Luft durch die Luftdurchlässe und durch die Einspritzöffnungen entlang den Brechkanten der ersten und zweiten spiralförmig gewundenen Schaufeln verbunden ist.

6. Verfahren nach einem der vorangehenden Ansprüche, dadurch gekennzeichnet, dass der Schritt zum Verflüssigen des Gipses in dem zumindest einen nachfolgenden Kessel das Bereitstellen einer gewobenen Matte in einem Boden des zumindest einen nachfolgenden Kessele und das Einspritzen eines Verflüssigungsmediums durch die Matte in dem Gips vorsieht, der in dem zumindest einen nachfolgenden Kessel enthalten ist.

7. Verfahren nach Anspruch 6, gekennzeichnet durch ein perforiertes Sieb, das mehrere Durchbrüche festlegt, die über der gewobenen Matte vorgesehen sind.

8. Verfahren nach Anspruch 6 oder 7, dadurch gekennzeichnet, dass die gewobene Matte aus Edelstahl gebildet ist.

9. Verfahren nach einem der vorangehenden Ansprüche, dadurch gekennzeichnet, dass der Schritt zum Verflüssigen des Gipses in dem zumindest einen nachfolgenden Kessel das Bereitstellen von mehreren Lufteinspritzdüsen um einen Umfang bzw. Rand des zumindest einen nachfolgenden Kessels und das Einspritzen eines Verflüssigungsmediums durch die mehreren Düsen zum Verflüssigen des Gipses in den zweiten und dritten Kesseln vorsieht.

10. Verfahren nach Anspruch 9, dadurch gekennzeichnet, dass die Lufteinspritzdüsen jeweils radial gerichtete Öffnungen und zumindest eine axial gerichtete Öffnung enthalten.

11. Verfahren nach einem der vorangehenden Ansprüche, dadurch gekennzeichnet, dass der zumindest eine nachfolgende Kessel einen zweiten Kessel und einen dritten Kessel umfasst, und dass die Schritte zum Erwärmen und Verflüssigen des Gipses das Erwärmen des Gipses in dem zweiten Kessel auf eine zweite vorbestimmte Temperatur höher als die erste vorbestimmte Temperatur und das Erwärmen des Gipses in dem dritten Kessel auf eine dritte vorbestimmte Temperatur höher als die zweite vorbestimmte Temperatur umfassen, wobei die dritte vorbestimmte Temperatur gleich der Endtemperatur ist.

12. Verfahren nach einem der vorangehenden Ansprüche, dadurch gekennzeichnet, dass die vorbestimmte Endtemperatur höher als etwa 480°C (etwa 900°F) ist.

13. Verfahren nach Anspruch 12, dadurch gekennzeichnet, dass der rückgewonnene Gips im wesentlichen aus unlöslichem Calciumsulfatanhydrit besteht.

14. Verfahren nach einem der Ansprüche 1 bis 11, dadurch gekennzeichnet, dass die vorbestimmte Endtemperatur geringer als etwa 480°C (etwa 900°F) ist, und dass der rückgewonnene Gips im wesentlichen aus unlöslichem Calciumsulfatanhydrit besteht.

15. Verfahren nach einem der vorangehenden Ansprüche, dadurch gekennzeichnet, dass die erste vorbestimmte Temperatur geringer als etwa 200°C (etwa 400°F) ist, und dass der gemahlene Gips, der aus dem ersten Kessel zum Überlaufen gebracht wird, im wesentlichen aus Calciumsulfathemihydrat besteht.

16. Verfahren nach einem der Ansprüche 11 bis 14, gekennzeichnet durch Überlaufen lassen des gemahlenen Gipses aus dem ersten Kessel und dem zweiten Kessel und Erwärmen des Gipses in dem zweiten Kessel auf eine zweite vorbestimmte Temperatur höher als die erste vorbestimmte Temperatur, während der Gips in dem zweiten Kessel gleichzeitig verflüssigt wird, durch Überlaufen lassen des Gipses aus dem zweiten Kessel in den dritten Kessel und Erwärmen des Gipses in dem dritten Kessel auf eine dritte vorbestimmte Temperatur höher als die zweite vorbestimmte Temperatur, während der Gips in den dritten Kessel gleichzeitig verflüssigt wird, und Rückgewinnen des Gipses aus dem dritten Kessel, der im wesentlichen aus Calciumsulfatanhydrit besteht.

17. Verfahren nach Anspruch 16, dadurch gekennzeichnet, dass die dritte vorbestimmte Temperatur höher als etwa 480°C (etwa 900°F) ist, und dass der rückgewonnene Gips im wesentlichen aus unlöslichem Calciumsulfatanhydrit besteht.

18. Verfahren nach Anspruch 16, dadurch gekennzeichnet, dass die dritte vorbestimmte Temperatur niedriger als etwa 480°C (etwa 900°F) ist, und dass der rückgewonnene Gips im wesentlichen aus löslichem Calciumsulfatanhydrit besteht.

19. Verfahren nach einem der Ansprüche 16 bis 18, dadurch gekennzeichnet, dass die erste vorbestimmte Temperatur etwa 120°C bis 190°C (etwa 250°F bis 380°F) beträgt, dass die zweite vorbestimmte Temperatur etwa 260°C bis 430°C (etwa 500°F bis 800°F) beträgt, und dass die dritte vorbestimmte Temperatur etwa 480°C bis 710°C (etwa 900°F bis 1300°F) beträgt.

20. Verfahren nach Anspruch 19, dadurch gekennzeichnet, dass die erste vorbestimmte Temperatur etwa 150°C (etwa 310°F) beträgt, dass die zweite vorbestimmte Temperatur etwa 320°C (etwa 600°F) beträgt, und dass die dritte vorbestimmte Temperatur etwa 540°C (etwa 1000°F) beträgt.

21. System zum Kalzinieren von Gips und zum Herstellen eines Anhydrit-Erzeugnisses, wobei das System aufweist:

Zumindest zwei Kessel ohne feuerfestem Stoff mit einer Kesselhülle, die eine Innenkammer zum Aufnehmen von gemahlenem Gips festlegt, wobei die zumindest zwei Kessel einen ersten Kessel und zumindest einen nachfolgenden Kessel aufweisen,

eine Heizeinrichtung, die in den zumindest zwei Kesseln angeordnet ist, um ein erwärmtes Medium durch die Innenkammer der zumindest zwei Kessel umzuwälzen, ohne dass das erwärmte Medium mit Gips in Kontakt gelangen kann, der in den zumindest zwei Kesseln enthalten ist;

eine Zuführeinrichtung zum Zuführen von gemahlenem Gips in den ersten Kessel;

eine Verbindungseinrichtung zum Überführen von erwärmtem gemahlenen Gips aus dem ersten Kessel in den zumindest einen nachfolgenden Kessel; und

eine Verflüssigungseinrichtung, die in dem zumindest einen nachfolgenden Kessel zum Verflüssigen des gemahlenen Gipses vorgesehen ist, der in diesem Kessel enthalten ist, wobei die Verflüssigungseinrichtung zumindest eine drehbare Schaufel mit mehreren Einspritzöffnungen entlang einer Brechkante aufweist, die in dem zumindest einen nachfolgenden Kessel vorgesehen ist, und eine Luftzufuhreinrichtung zum Einspritzen eines Verflüssigungsmediums durch die mehreren Einspritzöffnungen zum Verflüssigen des Gipses, der in dem zumindest einen nachfolgenden Kessel enthalten ist.

22. System nach Anspruch 21, dadurch gekennzeichnet, dass die zumindest eine Schaufel eine erste spiralförmig gewundene Schaufel und eine zweite spiralförmig gewundene Schaufel aufweist, die sich vertikal zwischen einer oberen und einer unteren horizontalen Schaufel erstrecken, und wobei die ersten und zweiten spiralförmig gewundenen Schaufeln jeweils ein Luftrohr entlang ihren Brechkanten aufweisen, die mehrere Einspritzöffnungen aufweist, die in dem zumindest einen nachfolgenden Kessel radial gerichtet sind, um ein Verflüssigungsmedium in den darin enthaltenen Gips einzuspritzen.

23. System nach Anspruch 22, dadurch gekennzeichnet, dass die Heizeinrichtung eine Brennerröhrenwicklung enthält, und dass die ersten und zweiten spiralförmig gewundenen Schaufeln vorauseilende Kanten vor den Brechkanten und nacheilende Kanten hinter den Brechkanten aufweisen, wobei die Einspritzöffnungen der Luftrohre an den Brechkanten in Richtung auf die Brennerwicklung gerichtet sind.

24. System nach Anspruch 22 oder 23, dadurch gekennzeichnet, dass die ersten und zweiten spiralförmig gewundenen Schaufeln und die oberen und unteren horizontalen Schaufeln auf einer zentralen Achse angebracht sind, und dass ein Paar von ersten und zweiten horizontalen Tragstangen vorgesehen sind, die sich zwischen der zentralen Achse und Zwischenabschnitten der ersten und zweiten spiralförmig gewundenen Schaufeln erstrecken.

25. System nach Anspruch 24, dadurch gekennzeichnet, dass die zentrale Achse und die Tragstangen Lufteinspritzdurchlässe aufweisen, und dass eine Luftquelle vorgesehen ist, die mit dem Luftdurchlass in der zentralen Achse verbunden ist, um Luft durch die Luftdurchlässe und durch die Einspritzöffnungen entlang den Brechkanten der ersten und zweiten spiralförmig gewundenen Schaufeln zu verteilen.

26. System nach einem der Ansprüche 21 bis 25, dadurch gekennzeichnet, dass die Verflüssigungseinrichtung außerdem eine gewobene Bahn oder Matte umfasst, die in einem Boden des zumindest einen nachfolgenden Kessels vorgesehen ist, und eine Luftquelle zum Einspritzen eines verflüssigten Mediums durch die gewobene Bahn oder Matte in den Gips, der in dem bzw. den nachfolgenden Kessel(n) enthalten ist.

27. System nach Anspruch 26, gekennzeichnet durch ein perforiertes Sieb, das mehrere Durchbrüche festlegt, die über der gewobenen Bahn bzw. Matte vorgesehen sind.

28. System nach Anspruch 26 oder 27, dadurch gekennzeichnet, dass die gewobene Bahn oder Matte aus Edelstahl gebildet ist.

29. System nach einem der Ansprüche 21 bis 28, dadurch gekennzeichnet, dass die Verflüssigungseinrichtung außerdem mehrere Einspritzdüsen umfasst, die über einen Umfang bzw. Rand der Kesselhülle(n) des zumindest einen nachfolgenden Kessels angeordnet sind, und dass eine Luftquelleneinrichtung vorgesehen ist, die mit den mehreren Düsen verbunden ist, um Luft durch die Düsen und in den Kesselinhalt einzuspritzen, um den darin enthaltenen Gips zu verflüssen.

30. System nach Anspruch 29, dadurch gekennzeichnet, dass die Einspritzdüsen mehrere radial gerichtete Öffnungen und zumindest eine axiale Öffnung umfassen.

31. System nach einem der Ansprüche 21 bis 30, dadurch gekennzeichnet, dass die zumindest zwei Kessel einen ersten, einen zweiten und einen dritten Kessel umfassen.

Revendications

1. Procédé de calcination du gypse pour produire un produit d'anhydrite, ledit procédé comprenant les étapes consistant à :

introduire du gypse broyé dans une première chaudière ;

chauffer le gypse broyé dans ladite première chaudière à une première température prédéterminée ;

faire déborder ledit gypse broyé de ladite première chaudière à au moins une chaudière suivante ;

chauffer ledit gypse dans ladite au moins une chaudière suivante jusqu'à une température finale supérieure à ladite première température prédéterminée tout en fluidisant simultanément ledit gypse dans ladite au moins une chaudière suivante ; et

récupérer ledit gypse de ladite au moins une chaudière suivante qui consiste essentiellement en de l'anhydrite de sulfate de calcium ;

ladite étape de fluidisation dudit gypse dans ladite au moins une chaudière suivante comprenant l'étape consistant à prévoir au moins une lame rotative ayant une pluralité d'orifices d'injection le long d'un bord d'attaque de celle-ci, dans ladite au moins une chaudière suivante, et à déplacer ladite au moins une lame dans ladite au moins une chaudière suivante tout en évacuant simultanément un milieu de fluidisation à travers ladite pluralité d'orifices d'injection pour fluidiser ledit gypse dans ladite au moins une chaudière suivante.

2. Procédé selon la revendication 1, caractérisé en ce que ladite au moins une lame comprend une première lame à torsion hélicoïdale et une seconde lame à torsion hélicoïdale s'étendant chacune entre une lame horizontale supérieure et inférieure, et en ce que lesdites première et seconde lames à torsion hélicoïdale comprennent chacune une canalisation d'air le long d'un bord de cassure de celle-ci ayant une pluralité d'orifices d'injection qui sont dirigés radialement pour injecter un milieu de fluidisation dans ledit matériau de gypse dans ladite au moins une chaudière suivante.

3. Procédé selon la revendication 2, caractérisé en ce que lesdites première et seconde lames à torsion hélicoïdale ont un bord d'attaque à l'avant dudit bord de cassure et un bord de sortie à l'arrière dudit bord de cassure.

4. Procédé selon la revendication 3, caractérisé en ce que lesdites première et seconde lames à torsion hélicoïdale et lesdites lames horizontales supérieure et inférieure sont montées sur un axe central, et en ce qu'une paire de première et seconde barres de support horizontales s'étendent entre ledit axe central et les parties intermédiaires desdites première et seconde lames à torsion hélicoïdale.

5. Procédé selon la revendication 4, caractérisé en ce que ledit axe central et lesdites barres de support comprennent chacun des passages d'air, et caractérisé par une source d'air qui est reliée audit passage d'air dans ledit axe central pour distribuer de l'air à travers lesdits passages d'air et à travers lesdits orifices d'injection le long des bords de cassure desdites première et seconde lames à torsion hélicoïdale.

6. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que ladite étape de fluidisation dudit gypse dans ladite au moins une chaudière suivante comprend l'étape consistant à prévoir un mat tissé au fond de ladite au moins une chaudière suivante et à injecter un milieu fluidisé à travers ledit mat et dans ledit gypse contenu dans ladite au moins une chaudière suivante.

7. Procédé selon la revendication 6, caractérisé en ce qu'un écran perforé qui définit une pluralité d'ouvertures est prévu sur ledit mat tissé.

8. Procédé selon la revendication 6 ou la revendication 7, caractérisé en ce que ledit mat tissé est formé en acier inoxydable.

9. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que ladite étape de fluidisation dudit gypse dans ladite au moins une chaudière suivante comprend l'étape consistant à prévoir une pluralité de buses d'injection d'air autour d'une périphérie de ladite au moins une chaudière suivante et à injecter un milieu de fluidisation à travers ladite pluralité de buses pour fluidiser ledit gypse dans lesdites deuxième et troisième chaudières.

10. Procédé selon la revendication 9, caractérisé en ce que lesdites buses d'injection d'air comprennent chacune des orifices dirigés radialement et au moins un orifice dirigé axialement.

11. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que ladite au moins une chaudière suivante comprend une deuxième chaudière et une troisième chaudière et en ce que les étapes de chauffage et de fluidisation dudit gypse comprennent le chauffage dudit gypse dans ladite deuxième chaudière à une deuxième température prédéterminée supérieure à ladite première température prédéterminée et le chauffage dudit gypse dans ladite troisième chaudière à une troisième température prédéterminée supérieure à ladite deuxième température prédéterminée, ladite troisième température prédéterminée étant égale à ladite température finale.

12. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que ladite température prédéterminée finale est supérieure à environ 480°C (environ 900°F).

13. Procédé selon la revendication 12, caractérisé en ce que ledit gypse récupéré consiste essentiellement en de l'anhydrite de sulfate de calcium insoluble.

14. Procédé selon l'une quelconque des revendications 1 à 11, caractérisé en ce que ladite température prédéterminée finale est inférieure à environ 480°C (environ 900°F) et en ce que ledit gypse récupéré consiste essentiellement en de l'anhydrite de sulfate de calcium soluble.

15. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que ladite première température prédéterminée est inférieure à environ 200°C (environ 400°F) et en ce que le gypse broyé qui déborde de ladite première chaudière consiste essentiellement en de l'hémihydrate de sulfate de calcium.

16. Procédé selon l'une quelconque des revendications 11 à 14, caractérisé par les étapes consistant à faire déborder ledit gypse broyé de ladite première chaudière à ladite deuxième chaudière et à chauffer ledit gypse dans ladite deuxième chaudière à une deuxième température prédéterminée supérieure à ladite première température prédéterminée tout en fluidisant simultanément ledit gypse dans ladite deuxième chaudière, à faire déborder ledit gypse de ladite deuxième chaudière à ladite troisième chaudière et à chauffer ledit gypse dans ladite troisième chaudière à une troisième température prédéterminée supérieure à ladite deuxième température prédéterminée tout en fluidisant simultanément ledit gypse dans ladite troisième chaudière, et à récupérer ledit gypse de ladite troisième chaudière qui consiste essentiellement en de l'anhydrite de sulfate de calcium.

17. Procédé selon la revendication 16, caractérisé en ce que ladite troisième température prédéterminée est supérieure à environ 480°C (environ 900°F) et en ce que ledit gypse récupéré consiste essentiellement en de l'anhydrite de sulfate de calcium insoluble.

18. Procédé selon la revendication 16, caractérisé en ce que ladite troisième température prédéterminée est inférieure à environ 480°C (environ 900°F) et en ce que ledit gypse récupéré consiste essentiellement en de l'anhydrite de sulfate de calcium soluble.

19. Procédé selon l'une quelconque des revendications 16 à 18, caractérisé en ce que ladite première température prédéterminée est d'environ 120°C à 190°C (environ 250°F à 380°F), en ce que ladite deuxième température prédéterminée est d'environ 260°C à 430°C (environ 500°F à 800°F), et en ce que ladite troisième température prédéterminée est d'environ 480°C à 710°C (environ 900°F à 1300°F).

20. Procédé selon la revendication 19, caractérisé en ce que ladite première température prédéterminée est d'environ 150°C (environ 310°F), en ce que ladite deuxième température prédéterminée est d'environ 320°C (environ 600°F), et en ce que ladite troisième température prédéterminée est d'environ 540°C (environ 1000°F).

21. Système de calcination du gypse et de production d'un produit d'anhydrite, ledit système comprenant :

au moins deux chaudières sans réfractaire ayant un corps de chaudière définissant une chambre intérieure pour retenir le gypse broyé, lesdites au moins deux chaudières comprenant une première chaudière et au moins une chaudière suivante ;

des moyens de chauffage disposés dans lesdites au moins deux chaudières pour faire circuler un milieu chauffé à travers ladite chambre intérieure desdites au moins deux chaudières sans permettre audit milieu chauffé de venir en contact avec le gypse contenu dans lesdites au moins deux chaudières ;

des moyens d'introduction pour introduire du gypse broyé dans ladite première chaudière ;

des moyens de communication pour transférer le gypse broyé chauffé de ladite première chaudière à ladite au moins une chaudière suivante ; et

des moyens de fluidisation prévus dans ladite au moins une chaudière suivante pour fluidiser le gypse broyé contenu à l'intérieur, lesdits moyens de fluidisation comprenant au moins une lame rotative ayant une pluralité d'orifices d'injection le long d'un bord de cassure de celle-ci prévue dans ladite au moins une chaudière suivante et des moyens d'amenée d'air pour injecter un milieu de fluidisation à travers ladite pluralité d'orifices d'injection pour fluidiser le gypse contenu dans ladite au moins une chaudière suivante.

22. Système selon la revendication 21, caractérisé en ce que ladite au moins une lame comprend une première lame à torsion hélicoïdale et une seconde lame à torsion hélicoïdale s'étendant verticalement entre une lame horizontale supérieure et une lame horizontale inférieure, et en ce que lesdites première et seconde lames à torsion hélicoïdale comprennent chacune une canalisation d'air le long des bords de cassure de celle-ci ayant une pluralité desdits orifices d'injection qui sont dirigés radialement dans ladite au moins une chaudière suivante pour injecter un milieu fluidisé dans ledit gypse contenu à l'intérieur.

23. Système selon la revendication 22, caractérisé en ce que lesdits moyens de chauffage comprennent un serpentin de tube de brûleur et en ce que lesdites première et seconde lames à torsion hélicoïdale ont des bords d'attaque à l'avant desdits bords de cassure et des bords de sortie à l'arrière desdits bords de cassure, lesdits orifices d'injection desdites canalisations d'air sur lesdits bords de cassure étant dirigés vers ledit serpentin de brûleur.

24. Système selon la revendication 22 ou la revendication 23, caractérisé en ce que lesdites première et seconde lames à torsion hélicoïdale et lesdites lames horizontales supérieure et inférieure sont montées sur un axe central, et en ce qu'une paire de première et seconde barres de support horizontales s'étend entre ledit axe central et les parties intermédiaires desdites première et seconde lames à torsion hélicoïdale.

25. Système selon la revendication 24, caractérisé en ce que ledit axe central et lesdites barres de support comprennent des passages d'injection d'air, et
caractérisé par une source d'air qui est reliée audit passage d'air dans ledit axe central pour distribuer de l'air à travers lesdits passages d'air et à travers les orifices d'injection le long des bords de cassure desdites première et seconde lames à torsion hélicoïdale.

26. Système selon l'une quelconque des revendications 21 à 25, caractérisé en ce que lesdits moyens de fluidisation comprennent en outre une nappe ou un mat tissé(e) prévu(e) dans le fond de ladite au moins une chaudière suivante et une source d'air pour injecter un milieu fluidisé à travers ladite nappe ou ledit mat tissé(e) et dans le gypse contenu dans la ou lesdites chaudières suivantes.

27. système selon la revendication 26, caractérisé en ce qu'un écran perforé qui définit une pluralité d'ouvertures est prévu sur ladite nappe ou ledit mat tissé(e).

28. Système selon la revendication 26 ou la revendication 27, caractérisé en ce que ladite nappe ou ledit mat tissé(e) est formé(e) en acier inoxydable.

29. Système selon l'une quelconque des revendications 21 à 28, caractérisé en ce que lesdits moyens de fluidisation comprennent en outre une pluralité de buses d'injection d'air disposées autour d'une périphérie du ou des corps de chaudière de ladite au moins une chaudière suivante, et caractérisé par des moyens de source d'air reliés à ladite pluralité de buses pour injecter de l'air à travers lesdites buses et dans le contenu de la chaudière pour fluidiser le gypse contenu à l'intérieur.

30. Système selon la revendication 29, caractérisé en ce que lesdites buses d'injection d'air comprennent une pluralité d'orifices dirigés radialement et au moins un orifice axial.

31. Système selon l'une quelconque des revendications 21 à 30, caractérisé en ce que lesdites au moins deux chaudières comprennent une première, une deuxième et une troisième chaudières.

Drawing